Is there a tool to accurately determine roof directions while editing? My approximations dont look good while rendering. An example is (britam tower in nairobi)
I always use JOSM to determine the correct roof direction. I draw a 90° angled line in the direction of the rain, and the number my arrow points to is the roof:direction of the skillion.
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Wow!
Thanks for that. Which josm tool do you use for that?
Most times, the direction is calculated by the longest side automaticly. A âroof:orientation=acrossâ may be needed.
Your example looks complex and a degeree would be the saver tagging.
This is standard line drawing (press a, click on the line you want to draw a 90° angle from, press a again. Youâll notice that the angle symbol becomes green when you press a that second time, and the text âAngle snapping activeâ is added:
Now hold ctrl and hover over that line until itâs marked yellow:
Now moving your mouse around will snap at certain angles, as you can see on my very first screenshot with the dotted yellow line.
That doesnât work for roof:shape=skillion, only for symmetrical roofs.
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What renderer do you use? Example way id?
Iâm not using a specific renderer, but Iâm testing most of my changes in OSM2World. Just quoting the wiki regarding roof:orientation if you donât believe me:
Well of course for squares donât have a defined âlongestâ. But your example abowe isnât one.
Thanks alot for the help! 
You quoted the OSM wiki: orientation and skillions donât work âfor squaresâ. Normally it works.
If you get me the OSM id I would do some checks.
It says
In the case of pent roofs (
skillion) [âŚ], capturing with roof:orientation is not suitable; roof:direction must be used here.
It cannot work, because the roof:orientation describes the orientation of the roof ridge. Since skillions are pretty much âone side of a hipped roofâ, you still need to say which side 
Well, you dropped âand square buildingsâ. Only square buildings donât work.
Sure, a skillion does not have a ridge, but a high corner, which is the same in this case.
And if a gabled building is an exact square, the orientation will have the same trouble
because the result is mathematical near undefined and may depend of the system, interpreting the Way.
I do write 3D rendering myself. Please give me an example ID to check it.
Oh, I just had a 2nd look at the wiki:
https://wiki.openstreetmap.org/wiki/Key:roof:orientation
âpent roofs (skillion ) and square buildingsâ
The âandâ in this case may not be meant boolean, but a human OR.
Anyway, I donât see why it should be a problem. Please show me examples.
No, neither square roofs nor skillion roofs work. I dropped the square, because you were misquoting me.
Exactly. But you still donât know which side that goes down that ridge you want to render: left or right. It only works for roofs which are symmetrical left and right the ridge, because then you can render both.
For for peace of mind, hereâs the ID of a building:part with a skillion: 1091004491. Of course you have a 50% chance to render the correct half of the roofâŚ
O, I see: If it is an exact rectangle, the âlongest sideâ is still near undefined. And for me, the longest side is the one, a skillion goes down from. Your example is quite clear about the longest side. So a renderer, following âMy Rulesâ 
will solve it.
In Passau are many skillions without directions. What do all renderer / OSM2World do? Follow âMy Ruleâ? But thatâs just a âbackupâ, the Wiki is a good advice anyway.
Hello,
Can anyone assist me in modelling of britam tower in nairobi. Ive tried this method but still does not look good. Just search britam tower in nairobi upper hill. Same with (rahimtulla tower)
The construction with building:part scillion is quite unusual, but looks almost correct.
I think the square symmetry of the parts is not exact, so the upper âceilingâ of them is not exact at the inner square. We need to have an WYSIWYG editor.
https://www.osmgo.org/v03.html?km=1&lat=-1.29984721&lon=36.81380474&ele=158.69&dir=95&view=-54